Method for aperiodic feedback of channel state information in a wireless access system supporting multi-carrier aggregation

ABSTRACT

The present invention relates to a wireless access system supporting multi-carrier aggregation (CA) and discloses various methods and devices for aperiodic feedback of channel state information (CSI). The method for aperiodic feedback of the channel state information (CSI) in the wireless access system supporting the multi-carrier aggregation (CA), according to an embodiment of the present invention, comprises the steps of: receiving a first message including an aperiodic CSI request field and uplink grant from a base station; receiving a second message including bitmap information indicating a downlink component carrier (DL CC) subjected to CSI measurement from the base station; measuring the CSI in consideration of at least one of the aperiodic CSI request, uplink grant, and bitmap information; and transmitting the measured CSI to the base station through a physical uplink shared channel (PUSCH) to thereby receive aperiodic feedback of the same.

This application is a continuation of Ser. No. 13/811,876 filed Jan. 23,2013, which is a 35 USC §371 National Stage entry of InternationalApplication No. PCT/KR2011/003390 filed on May 6, 2011, and claimspriority to U.S. Provisional Application Nos. 61/367,863 filed on Jul.26, 2010, 61/368,640 filed on Jul. 28, 2010, 61/407,433 filed Oct. 27,2010, 61/410,363 filed Nov. 5, 2010, and 61/416,740 filed Nov. 24, 2010,all of which are hereby incorporated by reference in their entireties asif fully set forth herein.

TECHNICAL FIELD

The present invention relates to a wireless access system supportingmulticarrier aggregation, and more particularly, to methods andapparatuses for aperiodically feeding back channel state information.

BACKGROUND ART

Wireless communication systems have been widely deployed to providevarious types of communication services such as voice or data services.Generally, a wireless communication system is a multiple access systemcapable of supporting communication with multiple users by sharingavailable system resources (bandwidth, transmit power, etc.). Multipleaccess systems include, for example, a Code Division Multiple Access(CDMA) system, a Frequency Division Multiple Access (FDMA) system, aTime Division Multiple Access (TDMA) system, an Orthogonal FrequencyDivision Multiple Access (OFDMA) system, and a Single Carrier FrequencyDivision Multiple Access (SC-FDMA) system.

DETAILED DESCRIPTION OF THE INVENTION Technical Problems

A 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)Rel-8 system (hereinafter, LTE system) uses a Multi-Carrier Modulation(MCM) scheme in which one Component Carrier (CC) is divided intomultiple bandwidths. However, a 3GPP LTE-Advanced system (hereinafter,LTE-A system) may use a Carrier Aggregation (CA) scheme in which one ormore CCs are aggregated in order to support a system bandwidth broaderthan a bandwidth of the LTE system.

Namely, since the LTE system does not configure a plurality of downlink(DL) CCs and/or uplink (UL) CCs, if a User Equipment (UE) is requestedto perform feedback, there is no ambiguity about for which CC feedbackis to be performed. In the LTE-A system, however, since a plurality ofCCs may be allocated to the UE in a CA situation in which a plurality ofDL/UL CCs is aggregated, it is not certain for which CC or serving cellfeedback is to be performed upon occurrence of an aperiodic feedbackrequest.

An object of the present invention devised to solve the above-describedproblem is to provide an efficient feedback method.

Another object of the present invention is to provide a method forimplicitly or explicitly designating a DL CC or a serving cell for whichfeedback is performed, when channel state information is aperiodicallyfed back.

Still another object of the present invention is to provide definitionof a UE behavior about for which DL CC a UE should report feedbackinformation to an eNB in a CA environment in which a plurality of DL CCsmay be present.

It will be appreciated by persons skilled in the art that that thetechnical objects that can be achieved through the present invention arenot limited to what has been particularly described hereinabove andother technical objects of the present invention will be more clearlyunderstood from the following detailed description.

Technical Solutions

The present invention discloses various methods and apparatuses foraperiodically feeding back channel state information in a wirelessaccess system supporting CA technology.

In one aspect of the present invention, a method for a User Equipment(UE) to aperiodically feed back Channel State Information (CSI) in awireless access system supporting multicarrier aggregation includesreceiving a first message including an aperiodic CSI request field andan uplink (UL) grant from a Base Station (BS), receiving a secondmessage including bitmap information indicating a downlink (DL)Component Carrier (CC) for which the CSI is to be measured, from the BS,measuring the CSI in consideration of one or more of the aperiodic CSIrequest field, the UL grant, and the bitmap information, andtransmitting the measured CSI to the BS through a Physical Uplink SharedChannel (PUSCH) to aperiodically feed back the measured CSI.

In another aspect of the present invention, a method for a Base Station(BS) to aperiodically receive feedback Channel State Information (CSI)in a wireless access system supporting multicarrier aggregation includestransmitting a first message including an aperiodic CSI request fieldand an uplink (UL) grant to a User Equipment (UE), transmitting a secondmessage including bitmap information indicating a downlink (DL)Component Carrier (CC) for which the CSI is to be measured, to the UE,and aperiodically receiving the CSI measured in consideration of one ormore of the aperiodic CSI request field, the UL grant, and the bitmapinformation through a Physical Uplink Shared Channel (PUSCH).

In a further aspect of the present invention, a User Equipment (UE) foraperiodically feeding back Channel State Information (CSI) in a wirelessaccess system supporting multicarrier aggregation includes a receptionmodule for receiving a radio signal, a transmission module fortransmitting the radio signal, and a processor for controlling aperiodicfeedback of the CSI, wherein the processor receives, using the receptionmodule from a Base Station (BS), a Physical Downlink Control Channel(PDCCH) signal including an aperiodic CSI request field and an uplink(UL) grant and a radio resource control signal including bitmapinformation indicating a downlink (DL) Component Carrier (CC) for whichthe CSI is to be measured, measures the CSI in consideration of one ormore of the aperiodic CSI request field, the UL grant, and the bitmapinformation, and transmits the measured CSI to the BS using thetransmission module through a Physical Uplink Shared Channel (PUSCH) toaperiodically feed back the CSI.

The UE may measure the CSI for one or more DL CCs indicated by thebitmap information, when the aperiodic CSI request field indicates thatthe CSI is to be measured for the DL CCs indicated by the bitmapinformation included in the second message.

The first message may be a Physical Downlink Control Channel (PDCCH)signal and the second message is a radio resource control signal of ahigher layer signal.

The first message may be transmitted through a UE-specific Search Space(USS) or a Common Search Space (CSS).

In the aspects of the present invention, if the aperiodic CSI requestfield indicates that the CSI is to be measured for a DL CC linked with aSystem Information Block 2 (SIB2), the UE may measure the CSI for the DLCC.

The above aspects of the present invention are merely some parts of theexemplary embodiments of the present invention and other embodimentsinto which the technical features of the present invention areincorporated can be derived and understood by those skilled in the artfrom the detailed description of the present invention which follows.

Advantageous Effects

The embodiments of the present invention have the following effects.

First, a UE can efficiently feed back channel state information to aneNB.

Second, when a UE aperiodically feeds back channel state information, aneNB explicitly or implicitly designates a DL CC or a serving cell forwhich feedback is performed and thus the UE can certainly discern forwhich DL CC or a serving cell channel quality measurement is to beperformed.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a radio frame structure which can beused in embodiments of the present invention;

FIG. 2 is a diagram illustrating a resource grid for one DL slot whichcan be used in embodiments of the present invention;

FIG. 3 is a diagram illustrating a DL subframe structure which can beused in embodiments of the present invention;

FIG. 4 is a diagram illustrating a UL subframe structure which can beused in embodiments of the present invention;

FIGS. 5(a) and 5(b) are diagrams explaining a multiband Radio Frequency(RF) based signal transmission and reception method used in an LTEsystem;

FIGS. 6(a) and 6(b) illustrate an exemplary method for managing aplurality of carriers in a plurality of MAC layers in an LTE system;

FIGS. 7(a) and 7(b) illustrate an exemplary method for managing one ormore carriers in a single MAC layer in an LTE system;

FIG. 8 is a diagram illustrating an exemplary CQI reporting method usedin an LTE system;

FIG. 9 is a diagram illustrating an exemplary feedback transmissionmethod using a CIF according to an embodiment of the present invention;

FIG. 10 is a diagram illustrating an aperiodic feedback method of CSIaccording to the number of DL CCs (or serving cells) for which feedbackis performed in a CA environment according to an embodiment of thepresent invention;

FIG. 11 is a diagram illustrating an aperiodic CSI reporting method in aCA environment according to an embodiment of the present invention; and

FIG. 12 is a diagram illustrating a UE and an eNB in which theembodiments of the present invention described with reference to FIG. 1to FIG. 11 can be performed, according to another embodiment of thepresent invention

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention disclose various methods fortransmitting and receiving a contention-based UL channel signal andapparatuses supporting the same.

The embodiments of the present invention described below arecombinations of elements and features of the present invention in apredetermined form. The elements or features are considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present invention may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present invention may be rearranged. Someconstructions of any one embodiment may be included in anotherembodiment and may be replaced with corresponding constructions orfeatures of another embodiment.

In the description of the attached drawings, procedures or steps will beomitted when it may obscure the subject matter of the present invention.In addition, procedures or steps that could be understood by thoseskilled in the art will not be described either.

In the embodiments of the present invention, a description is given ofdata transmission and reception between a BS and a terminal. Here, theBS refers to a terminal node of a network, which directly communicateswith the terminal. In some cases, a specific operation described asbeing performed by the BS may be performed by an upper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a terminal may be performed by the BS, or networknodes other than the BS. The term ‘BS’ may be replaced with terms suchas fixed station, Node B, eNode B (eNB), Advanced Base Station (ABS),access point, etc.

The term ‘terminal’ may be replaced with terms such as User Equipment(UE), Mobile Station (MS), Subscriber Station (SS), Mobile SubscriberStation (MSS), mobile terminal, Advanced Mobile Station (AMS), etc.

A transmitter is a fixed and/or mobile node that provides a data serviceor a voice service and a receiver is a fixed and/or mobile node thatreceives a data service or a voice service. Therefore, in UL, an MS mayserve as a transmitter and a BS may serve as a receiver. Similarly, inDL, the MS may serve as a receiver and the BS may serve as atransmitter.

The embodiments of the present invention can be supported by standarddocuments disclosed in at least one of wireless access systems includingan Institute of Electrical and Electronic Engineers (IEEE) 802.xxsystem, a 3rd Generation Partnership Project (3GPP) system, a 3GPP LTEsystem, and a 3GPP2 system. Especially, the embodiments of the presentinvention can be supported by 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS36.213, and 3GPP TS 36.321 documents. That is, obvious steps or portionsthat are not described in the embodiments of the present invention canbe explained with reference to the above documents. In additional, fordescription of all terms used herein, reference can be made to the abovestandard documents.

Reference will now be made in detail to the exemplary embodiments of thepresent invention in conjunction with the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention.

In addition, specific terms used in the embodiments of the presentinvention are provided to aid in understanding of the present inventionand those terms may be changed without departing from the spirit of thepresent invention.

The following technology can be used for a variety of radio accesssystems, for example, Code Division Multiple Access (CDMA), FrequencyDivision Multiple Access (FDMA), Time Division Multiple Access (TDMA),Orthogonal Frequency Division Multiple Access (OFDMA), and SingleCarrier Frequency Division Multiple Access (SC-FDMA) systems.

CDMA may be embodied through radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be embodiedthrough radio technology such as Global System for Mobile communications(GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be embodied through radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMax), IEEE 802-20, and Evolved UTRA(E-UTRA).

UTRA is a part of the Universal Mobile Telecommunications System (UMTS).3GPP Long Term Evolution (LTE) is a part of Evolved UMTS (E-UMTS)employing E-UTRA and uses OFDMA in DL and SC-FDMA in UL. An LTE-Advanced(LTE-A) system is an evolved version of a 3GPP LTE system. To clarifydescription of technical features of the present invention, although3GPP LTE/LTE-A is mainly described, the technical sprit of the presentinvention may be applied to IEEE 802.16e/m systems.

1. Basic Structure of 3GPP LTE/LTE-A System

FIG. 1 is a diagram illustrating a radio frame structure which can beused in embodiments of the present invention.

A radio frame includes 10 subframes and each subframe includes twoslots. A time for transmitting one subframe is defined as a TransmissionTime Interval (TTI). One subframe has a length of 1 ms and one slot hasa length of 0.5 ms.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain and a plurality ofResource Blocks (RBs) in the frequency domain. The OFDM symbolrepresents one symbol period in a 3GPP LTE system using an OrthogonalFrequency Division Multiplexing Access (OFDMA) scheme in DL. That is,the OFDM symbol may be called an SC-FDMA symbol or symbol periodaccording to a multiple access scheme. An RB is a resource allocationunit and includes a plurality of consecutive subcarriers per slot.

The radio frame structure shown in FIG. 1 is purely exemplary andvarious modifications may be made in the number of subframes included ina radio frame, the number of slots included in a subframe, and thenumber of OFDM symbols included in a slot.

FIG. 2 is a diagram illustrating a resource grid for one DL slot whichcan be used in embodiments of the present invention.

A DL slot includes a plurality of OFDM symbols in the time domain. Inthe illustrated example of FIG. 2, one DL slot includes 7 OFDM symbolsand one RB includes 12 subcarriers in the frequency domain.

Each element on a resource grid is referred to as a Resource Element(RE). One RB includes 12×7 REs. The number of RBs included in a DL slot,N^(DL), depends on DL transmission bandwidth configured in a cell.

FIG. 3 is a diagram illustrating a DL subframe structure which can beused in embodiments of the present invention.

A subframe includes two slots in the time domain. A maximum of 3 OFDMsymbols in the front portion of the first slot in a subframe correspondsto a control region to which control channels are allocated and theremaining OFDM symbols correspond to a data region to which a PhysicalDownlink Shared Channel (PDSCH) is allocated.

DL control channels used in a 3GPP LTE system include a Physical ControlFormat Indicator Channel (PCFICH), a Physical Downlink Control Channel(PDCCH), and a Physical Hybrid-ARQ Indicator Channel (PHICH). A PCFICHsignal transmitted on the first OFDM symbol of a subframe carriesinformation about the number of OFDM symbols (i.e. the magnitude of thecontrol region) used for control channel signal transmission in thesubframe. The PHICH carries an Acknowledgment/Negative-Acknowledgment(ACK/NACK) signal for a UL Hybrid Automatic Repeat Request (HARQ). Inother words, the ACK/NACK signal for UL data transmitted by a UE istransmitted over the PHICH.

DL control information transmitted through the PDCCH is referred to asDownlink Control Information (DCI). The DCI includes resource allocationinformation for a UE or a UE group and includes other controlinformation. For example, the DCI may include UL resource allocationinformation, DL resource allocation information, a UL transmit powercontrol command, etc.

The PDCCH may carry a transmission format and resource allocationinformation for a Downlink Shared Channel (DL-SCH), a transmissionformat and resource allocation information for an Uplink Shared Channel(UL-SCH), paging information on a Paging Channel (PCH), systeminformation on the DL-SCH, resource allocation information for ahigher-layer control message such as a random access responsetransmitted on the PDSCH, a transmit power control command set forindividual UEs in a UE group, a transmit power control command,information about activation of a Voice over Internet Protocol (VoIP),and the like.

A plurality of PDCCHs may be transmitted in one control region. A UE maymonitor a plurality of PDCCHs. The PDCCH is transmitted on one or moreconsecutive Control Channel Elements (CCEs). A CCE is a logicalallocation unit used to provide the PDCCH with a coding rate based on aradio channel state. The CCE corresponds to a plurality of ResourceElement Groups (REGs). A format of the PDCCH and the number of availablebits of the PDCCH are determined according to the correlation between acode rate provided in the CCE and the number of CCEs. An eNB determinesthe PDCCH format according to DCI to be transmitted to a UE and attachesa Cyclic Redundancy Check (CRC) to control information.

The CRC is masked together with a Radio Network Temporary Identifier(RNTI) according to the usage method or owner of the PDCCH. If the PDCCHis dedicated to a specific UE, an identifier of the UE (e.g. cell-RNTI(C-RNTI)) is masked to the CRC. If the PDCCH is dedicated to a pagingmessage, a paging identifier (e.g. paging-RNTI (P-RNTI)) is masked tothe CRC. If the PDCCH is for system information (especially, a systeminformation block), a system information identifier and a systeminformation RNTI (S-RNTI) may be masked to the CRC. A Random Access RNTI(RA-RNTI) may be masked to the CRC in order to indicate a random accessresponse to reception of a random access preamble of a UE.

In a CA environment, a PDCCH may be transmitted through one or more CCsand include resource allocation information for one or more CCs. Forexample, although the PDCCH is transmitted through one CC, the PDCCH mayinclude resource allocation information for one or more PDSCHs andPUSCHs.

FIG. 4 is a diagram illustrating a UL subframe structure which can beused in embodiments of the present invention;

Referring to FIG. 4, a UL subframe includes plural (e.g. two) slots.Each slot may include a different number of SC-FDMA symbols according tothe length of a Cyclic Prefix (CP). The UL subframe is divided into adata region and a control region in the frequency domain. The dataregion includes a Physical Uplink Shared Channel (PUSCH) and is used totransmit data signals including voice information. The control regionincludes a PUCCH and is used to transmit Uplink Control Information(DCI). The PUCCH includes an RB pair located at both ends of the dataregion in the frequency domain and is hopped using the slot as aboundary.

In an LTE system, a UE does not simultaneously transmit a PUCCH signaland a PUSCH signal in order to maintain a single carrier property.Nonetheless, in an LTE-A system, the PUCCH signal and the PUSCH signalmay be simultaneously transmitted in the same subframe according to atransmission mode of a UE and the PUCCH signal may be piggybacked on thePUSCH signal during transmission.

A PUCCH for one UE is allocated in an RB pair in a subframe and RBsbelonging to the RB pair occupy different subcarriers in two respectiveslots. Thus, the RB pair allocated to the PUCCH is frequency-hopped at aslot boundary.

The PUCCH may be used to transmit the following control information.

-   -   Scheduling Request (SR): SR is used for requesting UL-SCH        resources and is transmitted using an On-Off Keying (OOK)        scheme.    -   HARQ ACK/NACK: HARQ ACK/NACK is a response signal to a PDCCH        indicating a DL data packet or Semi-Persistent Scheduling (SPS)        release on a PDSCH. HARQ ACK/NACK indicates whether or not the        PDCCH indicating the DL data packet or SPS release has been        successfully received. A 1-bit ACK/NACK is transmitted as a        response to a single DL codeword and a 2-bit ACK/NACK is        transmitted as a response to two DL codewords. In the case of        TDD, ACK/NACK responses to a plurality of DL subframes are        gathered and transmitted on one PUCCH through bundling or        multiplexing.    -   Channel Quality Indicator (CQI) or Channel State Information        (CSI): CQI or CSI is feedback information for a DL channel.        Multiple Input Multiple Output (MIMO)-associated feedback        information includes a Rank Indicator (RI) and a Precoding        Matrix Indicator (PMI). 20 bits are used per subframe. In the        embodiments of the present invention, CSI may be interpreted as        including all of CQI, RI, and PMI.

The amount of UCI that can be transmitted in a subframe by a UE isdependent upon the number of SC-FDMA symbols available for UCItransmission. The SC-FDMA symbols available for UCI transmissionindicate the remaining SC-FDMA symbols other than SC-FDMA symbols thatare used for reference signal transmission in a subframe. In the case ofa subframe in which a Sounding Reference Signal (SRS) is configured, thelast SC-FDMA symbol of the subframe is also excluded. The referencesignal is used for coherent detection of a PUCCH. The PUCCH supports 7formats according to transmitted information.

Table 1 shows the mapping relationship between PUCCH and UCI for use inLTE.

TABLE 1 PUCCH Format UCI Format 1 Scheduling request (SR) Format 1a1-bit HARQ ACK/NACK with/without SR Format 1b 2-bit HARQ ACK/NACKwith/without SR Format 2 CQI (20 coded bits) Format 2 CQI and 1- or2-bit HARQ ACK/NACK for extended CP Format 2a CQI and 1-bit HARQACK/NACK Format 2b CQI and 2-bit HARQ ACK/NACK

2. Multicarrier Aggregation Environment

(1) Overview

A communication environment considered in the embodiments of the presentinvention includes all environments supporting multicarrier aggregation.That is, a multicarrier system or a carrier aggregation system used inthe present invention refers to a system configuring a target widebandby aggregating more than one carrier having a bandwidth narrower than atarget bandwidth in order to support a wideband.

In the present invention, multiple carriers indicate aggregation of CCs(or CA). In this case, CA refers to not only aggregation of contiguouscarriers but also aggregation of non-contiguous carriers. Multicarrieraggregation is interchangeably used with the term CA or bandwidthaggregation.

In an LTE-A system, the goal of multicarrier aggregation (i.e. CA) inwhich two or more CCs are aggregated is to support up to a bandwidth of100 MHz. When more than one carrier having a bandwidth narrower than atarget bandwidth is aggregated, the bandwidth of each aggregated carriermay be restricted to a bandwidth used in a legacy system in order tomaintain backward compatibility with a legacy IMT system.

For example, a legacy 3GPP LTE system may support bandwidths of {1.4, 3,5, 10, 15, 20}MHz and a 3GPP LTE-A system may support a bandwidth widerthan 20 MHz, using only the above bandwidths supported in the LTEsystem. A multicarrier system used in the present invention may supportCA by defining a new bandwidth irrespective of the bandwidths used inthe legacy system.

FIG. 5 is a diagram explaining a multiband Radio Frequency (RF) basedsignal transmission and reception method used in an LTE system.

In FIG. 5(a), one Medium Access Control (MAC) layer of a transmitter anda receiver may manage a plurality of carriers in order to efficientlyuse multiple carriers. To effectively transmit and receive multiplecarriers, it is assumed that both the transmitter and the receiver arecapable of transmitting and receiving the multiple carriers. FrequencyCarriers (FCs) managed by one MAC layer are flexible in terms ofresource management because they need not be contiguous. That is, it ispossible to configure both contiguous carrier aggregation andnon-contiguous carrier aggregation.

In FIG. 5(a) and FIG. 5(b), PHY0, PHY1, . . . , PHY n−2, and PHY n−1indicate multiple bands according to this technology and each band mayhave a Frequency Allocation (FA) size allocated for a specific serviceaccording to a predetermined frequency policy. For example, PHY0 (RFcarrier 0) may have an FA size allocated for a general FM radiobroadcast and PHY1 (RF carrier 1) may have an FA size allocated formobile phone communication.

To transmit signals through multiple bands as illustrated in FIG. 5(a)and to receive signals through multiple bands as illustrated in FIG.5(b), each of the transmitter and the receiver needs to include an RFmodule for transmitting and receiving signals through multiple bands. InFIG. 1 (FIG. 5??), a method of configuring MAC is determined by an eNBirrespective of DL or UL.

In brief, this technology is a signal transmission/reception technologyin which one MAC entity (hereinafter, simply referred to as “MAC” unlesssuch use causes confusion) manages/operates a plurality of RF carriers(or radio frequencies). RF carriers managed by one MAC need not becontiguous. Therefore, this technology has an advantage of highflexibility in terms of resource management.

FIG. 6 illustrates an exemplary method for managing a plurality ofcarriers in a plurality of MAC layers in an LTE system.

FIG. 6(a) illustrates a one-to-one mapping relationship between MAClayers and Physical (PHY) layers, when a transmitter (e.g. an eNB)supports multiple carriers, and FIG. 6(b) illustrates a one-to-onemapping relationship between MAC layers and PHY layers, when a receiver(e.g. a UE) supports multiple carriers. One PHY layer may use onecarrier.

FIG. 7 illustrates an exemplary method for managing one or more carriersin a single MAC layer in an LTE system.

In FIG. 7, one MAC layer may be mapped independently to one PHY layerfor each of specific carriers (e.g. carrier 0 and carrier 1) or one MAClayer may be mapped to PHY layers for specific carriers (e.g. carriern−1 (??n−2) and carrier n−1). If this hybrid mapping scheme is used,some carriers for which one MAC layer is mapped to a plurality of PHYlayers may be multiplexed in the method of FIG. 6 (??FIG. 5).

Referring to FIG. 7, FIG. 7(a) illustrates a one-to-one or one-to-m(m>1) mapping relationship between MAC layers and PHY layers, when atransmitter (e.g. an eNB) supports multiple carriers. FIG. 7(b)illustrates a one-to-one or one-to-m mapping relationship between MAClayers and PHY layers, when a receiver (e.g. a UE) supports multiplecarriers.

In a system supporting multiple carriers, different UEs may usedifferent carriers according to the capabilities of an eNB and the UEs.Notably, the carrier band support capabilities of the eNB may beconstantly fixed. The eNB may negotiate with the UEs to determinewhether to support carriers during call setup according to thecapabilities of the eNB.

A TDD system is configured to operate N carriers each including DL andUL transmissions. An FDD system is configured to use a plurality ofcarriers in each of UL and DL. In an LTE Rel-8 system, while thebandwidths of carriers in UL and DL may be different from each other,transmission and reception in a single carrier is basically supported.However, in an LTE-A system, a plurality of carriers may be operatedthrough CA. Furthermore, the FDD system may support asymmetrical CA inwhich the numbers of aggregated carriers/the bandwidths of aggregatedcarriers in UL and DL are different from each other.

An LTE-A UE disclosed in the present invention may simultaneouslymonitor RF signals on one or more CCs according to capabilities thereof.However, an LTE UE (e.g. an LTE Rel-8 UE) may transmit and receive RFsignals only on one CC according to the structure of a CC provided inthe LTE Rel-8 system. All CCs of LTE Rel-8 should be compatible witheach other, at least when the numbers of aggregated CCs in UL and DL arethe same. Consideration of non-compatible configurations of LTE-A CCs isnot precluded.

L1 (PHY) specification should support CA for contiguous andnon-contiguous CCs each including a maximum of 110 RBs using LTE Rel-8numerology. For details of a frequency spacing between contiguouscarriers in contiguous CA, reference may be made to RAN WG4specification. The RAN WG4 specification provides details of the numberof RBs supported per CC and guard bands necessary for specific CA. Ifpossible, it is desirable to apply the details of the RAN WG4specification to the L1 specification for contiguous CA andnon-contiguous CA.

A UE may be configured to support multiple carriers aggregated by adifferent number of CCs so as to have different bandwidths in UL and DL.In a typical TDD deployment, the bandwidths of CCs and the numbers ofCCs in DL and UL may be the same. RAN WG 4 will study combinations ofaggregated CCs and bandwidths.

From a UE perspective, one transport block without spatial multiplexingand one HARQ entity per scheduled CC may be considered. Each transportblock may be mapped only to a single CC. The UE may be simultaneouslyscheduled on a plurality of CCs.

(2) Compatibility of LTE-A System

In an LTE-A system, there is a backward compatible carrier whichsupports a legacy system (e.g. an LTE system). The backward compatiblecarrier should be accessible by UEs of all LTE releases. The backwardcompatible carrier can be operated as a single carrier or a part ofmultiple carriers (CA). In FDD, the backward compatible carrier alwaysoccurs in pairs in DL and UL.

In the LTE-A system, there is a non-backward compatible carrier whichdoes not support the legacy system. Legacy LTE UEs are unable to use thenon-backward compatible carrier but LTE-A UEs may use the non-backwardcompatible carrier. The non-compatible carrier can be operated as asingle carrier from the duplex distance and, otherwise, can be operatedas a part of CA.

The LTE-A system can support an extension carrier. The extension carriercannot be operated as a single carrier. However, if at least one carrierin a set of CCs is a single carrier, the extension carrier is operatedas a part of the set of CCs.

(3) Cell-Specific Linkage and UE-Specific Linkage

In CA, one or more carriers are used for two methods of cell-specificlinkage and UE-specific linkage. In the present invention, the term“cell-specific linkage” refers to CA from the perspective of a cell oran eNB and is expressed by the term “cell-specific” for convenience. Ifa cell means one backward or non-backward compatible carrier, the term“cell-specific” may be used to signify one or more carriers or resources(managed by a certain eNB) including one carrier represented by a cell.

Cell-specific DL/UL linkage may be a form of CA configured by an eNB ora cell. In the cell-specific DL/UL linkage, DL and UL linkage may bedetermined according to preset default Tx-Rx separation defined in theLTE Rel-8 system and/or the LTE-A system, in case of FDD. As an example,for default Tx-Rx separation of the LTE Rel-8 system, reference may bemade to sections 5.7.3 and 5.7.4 of 3GPP TS 36.101 V8.8.0. If Tx-Rxseparation only for the LTE-A system is defined, the cell-specific DL/ULlinkage may be defined according to the corresponding linkage. Fordefault Tx-Rx separation of the LTE-A system, reference may be made tosections 5.7.3 and 5.7.4 of 3GPP TS 36.101 V10.0.0.

UE-specific multicarrier (UE-specific DL/UL linkage) refers toconfiguring a CA type for use in a specific UE or UE group using anarbitrary method (e.g. UE capabilities, negotiation, signaling, and/orbroadcasting, etc.) between a UE and an eNB. For example, UE-specificDL/UL linkage defined in the LTE-A system includes a UE DL CC set and aUE UL CC set. The UE DL CC set, which is a set of DL CCs configured bydedicated signaling, is scheduled for reception of a PDSCH in DL. The UEUL CC set is scheduled on UL CCs to transmit a PUSCH in UL. InUE-specific DL/UL linkage, CC sets such as a PDCCH monitoring set and ameasurement set may be defined.

The PDCCH monitoring set may be configured in a UE DL CC set separatelyfrom a UE DL/UL CC set, in a form including a part of the UE DL CC set,or on CCs different from the UE DL CC set. The PDCCH monitoring set maybe UE-specifically or cell-specifically configured.

The measurement set increases according to the number of carriers withwhich a measurement result that a UE should report is aggregated as CAis introduced. The measurement set may be defined to reduce such reportoverhead or to effectively support measurement according to capabilitiesof each UE.

The UE-specific DL/UL linkage may be configured (1) irrespective ofcell-specific DL/UL linkage or (2) within a range for maintaining thestructure of cell-specific DL/UL linkage, in terms of flexibility.

As described above, the LTE-A system uses the concept of a cell tomanage radio resources. The cell is defined as a combination of a DLresource and a UL resource and the UL resource may be selectivelydefined. Accordingly, the cell may be configured by the DL resourcealone or by the DL resource and the UL resource. When multiple carriers(i.e. CA) are supported, the linkage between the carrier frequency (orDL CC) of the DL resource and the carrier frequency (or UL CC) of the ULresource may be indicated by system information.

A cell used in the LTE-A system includes a Primary cell (PCell) and aSecondary cell (SCell). The PCell may refer to a cell operating on aprimary frequency (or primary CC) and the SCell may refer to a celloperating on a secondary frequency (or secondary CC). Notably, only onePCell and one or more SCells may be allocated to a specific UE.

The PCell is used to perform an initial connection establishmentprocedure or a connection re-establishment procedure. The PCell mayrefer to a cell indicated during a handover procedure. The SCell can beconfigured after Radio Resource Control (RRC) connection is establishedand may be used to provide additional radio resources.

The PCell and SCell may be used as a serving cell. In case of a UE inwhich CA is not configured or CA is not supported even in anRRC_CONNECTED state, only a single serving cell comprised of only aPCell is present. Meanwhile, in case of a UE in which CA is configuredin an RRC_CONNECTED state, one or more serving cells may be present andentire cells include a PCell and one or more SCells.

After an initial security activation procedure is started, an E-UTRANmay configure a network including one or more SCells in addition to aninitially configured PCell during a connection establishment procedure.In a multicarrier environment, each of a PCell and an SCell may serve asa CC. Namely, CA may be understood as a combination of a PCell and oneor more SCells. In the following embodiments, a Primary CC (PCC) mayhave the same meaning as a PCell and a Secondary CC (SCC) may have thesame meaning as an SCell.

3. MIMO Feedback

A radio access system supporting multicarrier aggregation used in theembodiments of the present invention may also support a MIMO feedbackmethod using two or more input/output antennas.

MIMO feedback information includes a Precoding Matrix Index (PMI), aRank Indicator (RI), and a Channel Quality Information (CQI) index. TheRI is determined from the number of assigned transmission layers and aUE may obtain an RI value from associated DCI. The PMI is defined in TS36.211. An SINR for each PMI is calculated and the SINR is transformedinto capacity. The best PMI may be selected based on the capacity. TheCQI represents channel quality and the CQI index indicates channelcoding rate and a modulation scheme.

Table 2 shows an exemplary CQI table used in the LTE system.

TABLE 2 CQI index Modulation Coding rate*1024 Efficiency 0 1 QPSK 780.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4 QPSK 308 0.6016 5 QPSK 4490.8770 6 QPSK 602 1.1758 7 16QAM 378 1.4766 8 16QAM 490 1.9141 9 16QAM616 2.4063 10 64QAM 466 2.7305 11 64QAM 567 3.3223 12 64QAM 666 3.902313 64QAM 772 4.5234 14 64QAM 873 5.1152 15 64QAM 948 5.5547

If MIMO is applied to a system, the number of necessary CQI also varies.A MIMO system generates multiple channels using multiple antennas andthus a plurality of codewords may be used. Accordingly, a plurality ofCQI should be used and, in this case, the amount of control informationproportionally increases.

A UE selects the highest CQI index from among CQI values with atransport Block Error Rate (BLER) not exceeding 0.1 in a systembandwidth and feeds back the highest CQI to an eNB. MIMO feedbacktransmission of a CQI-only mode serves to transmit aperiodic CQI througha PUSCH and, in this case, no PUSCH data is transmitted. The eNB maytransmit DCI format 0 to the UE in order to request aperiodic CQI.

FIG. 8 is a diagram illustrating an exemplary CQI reporting method usedin an LTE system.

Referring to FIG. 8, CQI reporting is divided into periodic reportingand aperiodic reporting. Periodic CQI reporting refers to reporting ofchannel quality to an eNB from a UE at a predetermined time withoutadditional signaling, whereas aperiodic CQI reporting refers torequesting the UE to report CQI through explicit signaling according tothe necessity of a network.

Periodic CQI reporting of the UE is performed through a PUCCH. Forperiodic CQI reporting of the UE through the PUCCH, the UE should uselimited bits compared with CQI reporting through a PUSCH. A recentlytransmitted RI may be used to calculate wideband CQI/PMI.

If aperiodic CQI reporting is needed, the network signals a ULscheduling grant using DCI format 0 to the UE. The UE performs aperiodicCQI reporting when a CQI request value of DCI format 0 is 1. AperiodicCQI reporting (i.e. CQI request=1) is divided into a CQI-only(transmission) mode and a CQI+data (transmission) mode.

For example, if the CQI request value is 1, an MCS index IMCS is 29, andthe number of allocated Physical Resource Blocks (PRBs) is less than 4(i.e. NPRB≦4), the UE interprets corresponding signaling as the CQI-onlymode and, otherwise, the UE interprets corresponding signaling as theCQI+data mode. In the CQI-only mode, the UE transmits only CSI throughthe PUSCH without data (i.e. a UL-SCH transport block). On the otherhand, in the CQI+data mode, the UE transmits both the CSI and datathrough the PUSCH. The CQI-only mode may be generalized as afeedback-only mode and the CQI+data mode may be referred to as afeedback+data mode. The CSI includes at least one of CQI, PMI, and RI.

If periodic CQI reporting and aperiodic CQI reporting are scheduled tobe simultaneously performed in the same subframe, the UE performs onlyaperiodic CQI reporting. If data transmission through the PUSCH isscheduled, the same PUCCH based reporting format is used on the PUSCH.RI in a PUCCH reporting mode is independent of RI in a PUSCH reportingmode. RI in the PUSCH reporting mode is valid only for CQI/PMI in thePUSCH reporting mode.

4. Aperiodic Feedback Reporting Method

The LTE system may perform an aperiodic feedback request through twomethods. One is a method using a CQI request field included in DCIformat 0 and the other is a method using a CQI request field included ina random access grant. In the embodiments of the present invention, themethod using the CQI request field of DCI format is explained forconvenience of description.

An eNB sets the CQI request field included in DCI format 0 to ‘1’ andtransmits a PDCCH signal including the corresponding DCI format 0 to aUE in an n-th subframe. In case of FDD, the UE transmits CQI/RI/PMIfeedback to the eNB through a PUSCH signal in an (n+4)-th subframe. Incase of TDD, the UE transmits CQI/RI/PMI feedback to the eNB in an(n+k)-th subframe. For k values, reference may be made to Table 8-2 of3GPP TS 36.213. During aperiodic feedback reporting, a minimum period isone subframe and the size of a subband for CQI may be set to have thesame configuration as Tx-Rx configuration.

The UE is configured to set transmission modes for feedback for channelstates through higher layer signaling with the eNB in advance. Refer tothe following Table 3 for details of the transmission modes forfeedback.

TABLE 3 PMI Feedback Type No PMI Single PMI Multiple PMIs PUSCH WidebandMode 1-2 feedback (wideband CQI) type UE Selected Mode 2-0 Mode 2-2(subband CQI) Higher layer Mode 3-0 Mode 3-1 configured (subband CQI)

In Table 3, for a detailed description of each transmission mode,reference may be made to 3GPP TS 36.213. A feedback mode is set inassociation with a currently configured DL transmission mode and thefeedback mode which can be supported according to each DL transmissionmode may be summarized as follows.

-   -   Transmission mode 1: Modes 2-0, 3-0    -   Transmission mode 2: Modes 2-0, 3-0    -   Transmission mode 3: Modes 2-0, 3-0    -   Transmission mode 4: Modes 1-2, 2-2, 3-1    -   Transmission mode 5: Mode 3-1    -   Transmission mode 6: Modes 1-2, 2-2, 3-1    -   Transmission mode 7: Modes 2-0, 3-0

In order for the UE to transmit UL data and control signals through thePUSCH, the eNB should transmit a UL grant message to the UE through a DLPDCCH. In the LTE system, the eNB transmits a UL grant to the UE throughtransmission of a PDCCH signal defined as DCI format 0. If a pluralityof UL carriers (or serving cells) is present, the eNB may designate a ULCC on which the eNB wishes to transmit a PUSCH signal by including acarrier index value defined in a Carrier Indication Field (CIF) in aninformation field of DCI transmitted on a PDCCH.

While the CIF may vary with the number of CCs that the CIF shouldindicate, it is desirable to include the CIF in a predetermined positionof a DCI format with a fixed size (e.g. 3 bits) in order to reduceburden on Blind Decoding (BD) upon reception of a PDCCH of the UE.

FIG. 9 is a diagram illustrating an exemplary feedback transmissionmethod using a CIF according to an embodiment of the present invention.

In FIG. 9, a method for transmitting a PUSCH signal through a CIF in aCA environment is illustrated. A Carrier Indication (CI) value may beUE-specifically defined. For instance, a UE x that is communicating withan eNB comprised of a total of N DL CCs and M UL CCs may have aUE-specifically configured CC set of n DL CCs and m UL CCs. In this CCset, DL/UL CCs may have UE-specific CI values. If the eNB transmitsPDCCH DCI format 0 including one CI value among 1 to m in a subframe n(S910), the UE may transmit a PUSCH signal on a UL CC indicated by theCI value in a subframe n+4 (in case of FDD) (S920).

In FIG. 9, if a corresponding PDCCH i is transmitted with a CQI requestset to ‘1’ to the UE, the UE recognizes that a corresponding request isan aperiodic feedback request and may transmit a feedback value to theeNB through the PUSCH signal. In this case, if the UE aperiodicallytransmits feedback information for one or more DL CCs to the eNB throughone specific UL CC, the UE should discern DL CCs and/or UL CCs for whichaperiodic feedback is performed. That is, a multicarrier aggregationenvironment may include a plurality of DL CCs and UL CCs and, therefore,it is necessary to define UE behavior regarding which DL CCs feedbackinformation should be reported to the eNB.

FIG. 10 is a diagram illustrating an aperiodic feedback method of CSIaccording to the number of DL CCs (or serving cells) for which feedbackis performed in a CA environment according to an embodiment of thepresent invention.

Hereinafter, a method for configuring DL CCs for which feedback isperformed according to the number of DL CCs for feedback in a CAenvironment will be described. An eNB and/or a UE may select one or moreDL CCs or serving cells for which CSI feedback is performed.

Referring to FIG. 10, an eNB may inform UEs supporting CA as to whetheronly one DL CC for which CSI is to be fed back is scheduled or two ormore DC CCs for which CSI is to be fed back are scheduled, throughhigher layer (e.g. RRC) signaling. The eNB may inform the UE ofinformation about the DL CCs according to Quality of Service (QoS) ofthe UE, CA capabilities, cell load, and/or cross-carrierscheduling/cross-carrier non-scheduling (S1010).

Through step S1010, the UE may obtain in advance information aboutwhether the number of DL CCs (or serving cells) for which CSImeasurement is performed is one or more than one and the UE may feedback CSI to the eNB according to a CSI reporting method thereof.

The eNB may inform the UE of DL CCs or serving cells for which aperiodicfeedback is to be performed through a UL grant or a CIF included in aPDCCH signal (step S1020).

In step S1020, the DL CCs for which aperiodic feedback is performed maybe explicitly or implicitly signaled to the UE and detailed signalingmethods will be described later.

The UE may confirm one DL CC or serving cell or two or more DL CCs orserving cells, for aperiodic feedback (S1030) and may measure channelquality for a corresponding DL CC or DL CCs (S1040).

While CSI for one DL CC is transmitted through one PUSCH in an LTEsystem which does not support CA, CSI for two or more DL CCs may betransmitted in an LTE-A system which supports CA. Accordingly, since itis assumed that the UE in FIG. 10 supports CA, the UE may report CSI forchannel quality measured for one or more DL CCs to the eNB using a PUSCHsignal (S1050).

In step S1050, in order for the UE to transmit CSI having the increasedamount of information according to channel quality measurement for twoor more DL CCs, the following two methods may be considered.

The first method is time multiplexing. Time multiplexing is the sameconcept as cycling and transmits CSI for N DL CCs not in one subframebut in a maximum of N subframes. As the simplest example, CSI for DL CC#0 is transmitted in an n-th subframe, CSI for DL CC #1 is transmittedin an (n+1)-th subframe, and CSI for an N-th DL CC #N is transmitted inan (n+N)-th subframe. At this time, subframes in which CSI istransmitted may be configured continuously or non-continuously with aspecific offset. Alternatively, the UE may aperiodically transmit CSIfor one or more DL CCs in one subframe through a PUSCH.

The second method is joint coding. Joint coding serves to transmit CSIfor one or more DL CCs in one subframe. In this case, the UE may useextended frequency resources for aperiodic CSI reporting and mayjoint-code CSI for DL CCs to transmit the joint-coded DL CCs through onePUSCH.

In the embodiment of the present invention, step S1010 may beselectively used. If step S1010 is not used, the UE may measure CSI onlyfor DL CCs indicated in step S1020 and report a measurement result tothe eNB.

Hereinbelow, methods for configuring and scheduling (1) only one DL CCand (2) two or more DL CCs, for which feedback is performed, in stepsS1020 to S1050, will be described.

(1) When Only One DL CC is Configured for Feedback

For example, when only one DL CC is configured for feedback, the targetDL CC may be selected as one of {circle around (1)} a DL CC receiving aUL grant including aperiodic CQI report information, {circle around (2)}a DL CC linked with a UL CC on which a PUSCH indicated by a UL grant isto be transmitted through a System Information Block 2 (SIB2), {circlearound (3)} a DL PCC, {circle around (4)} a DL CC allocated andconfigured through higher layer (e.g. RRC layer) signaling, and {circlearound (5)} a DL CC allocated implicitly for CQI measurement.

Hereinbelow, the above case {circle around (2)} will be described indetail.

The SIB2 may include shared channel information, random access channelinformation, random access preamble information, and HARQ information.The SIB2 may include information about a UL shared channel (e.g. UL CC)which may be linked with one or more DL CCs.

A DL heavy case in which a plurality of DL CCs is allocated to one UL CChas a disadvantage of feeding back only CSI for only one DL CC, if thenumber of DL CCs having SIB2 linkage with a UL CC is one and the SIB2linked DL CC is configured for CSI feedback. Accordingly, in this case,it is desirable that another DL CC be configured for feedback inaddition to the SIB2 linked DL CC.

As a first example, when the eNB transmits a UL grant including a CIF tothe UE, the eNB may use the CIF to indicate a DL CC for feedback ratherthan a UL CC. Since this case corresponds to a DL heavy case, only oneUL CC is present. Accordingly, the UE may feed back CSI for one of anSIB2 linked DL CC and a DL CC indicated by the CIF to the eNB throughthe PUSCH.

As a second example, when the eNB transmits a UL grant including a CIFto the UE, the eNB may use the CIF to indicate a DL CC for feedback.That is, the UE may report CSI for a DL CC adjacent to a DL CC indicatedby the CIF to the eNB in a TDD form according to a specific criterion ofcarrier index order or frequency order (e.g. in ascending/descendingorder) based on the DL CC indicated by the CIF.

As a third example, the UE may use a hybrid form of the first and secondmethods.

As a fourth example, a virtual SIB2 linked DL CC may be configured forfeedback. For example, a DL CC which has no SIB2 linkage may beconfigured to have a virtual SIB2 linkage with a UL CC. This virtualSIB2 linkage may be explicitly configured by higher layer (e.g. RRC)signalling or may be implicitly determined. When aperiodic CSI reportingis triggered, the UE may report CSI feedback for SIB2 linked DL CCs orCSI feedback for a DL CC which has virtual SIB2 linkage with a single ULCC to the eNB.

Namely, a DL CC which has no SIB2 linkage may be configured to havevirtual SIB2 linkage. Such virtual SIB2 linkage may be indicated to theUE explicitly by higher layer signalling or implicitly. For example,virtual SIB2 linkage may be implicitly indicated in ascending ordescending order using carrier index, cell index, CIF order, and/orfrequency index from an original SIB2 linked DL CC.

If virtual SIB2 linkage is configured and an aperiodic CSI report isrequested, the UE may transmit CSI feedback for one of the original SIB2linked DL CC and a virtual SIB2 linked DL CC to the eNB. If there is aremaining code point without being used in a CIF included in a UL grant(e.g. if a CIF is 3 bits, up to 8 states can be expressed and, ifremaining states or bits are present after setting states for DL/UL CCindication, they may be used for code points), whether to transmitfeedback for the original SIB2 linked DL CC or to transmit feedback forthe virtual SIB2 linked DL CC may be indicated using the code points. Ifmore states remain in the CIF so as to be used for code points, the eNBmay inform the UE of one of the original SIB2 linked DL CC or thevirtual SIB2 linked DL CC for which CSI feedback is to be performed.

As described above, when a 3-bit CIF is used to indicate not an SIB2linked DL CC or UL CC but other DL CCs, a 1-bit CIF may remain. In thiscase, the eNB may inform the UE using the remaining 1-bit CIF of whetherto report CSI feedback for a DL CC indicated by the CIF, to report CSIfeedback for an SIB2 linked DL CC, or to report CSI feedback for all DLCCs.

A method for feeding back CSI for {circle around (5)} a DL CC allocatedimplicitly for CQI measurement will be described below.

If a DL CC which has SIB2 linkage with a UL CC indicated by a UL grantused for an aperiodic CSI request is used for CSI measurement andreporting, the DL CC which has SIB2 linkage with the corresponding UL CCis explicitly used for aperiodic CSI measurement and reporting. However,a DL CC which has no SIB2 linkage with a UL CC cannot perform aperiodicCSI triggering. An implicit rule capable of performing aperiodic CSItriggering for such a DL CC is proposed.

For example, the UE may perform CSI measurement and reporting for a DLCC adjacent to an SIB2 linked DL CC or to a DL CC indicated by a CIF.That is, if aperiodic CSI for specific DL CC #1 is triggered, the eNBand UE may configure a DL CC or serving cell having a carrier index orcell index adjacent to the corresponding DL CC as a DL CC or servingcell for aperiodic CSI measurement and reporting without explicitindication.

In the embodiments of the present invention, an explicit DL CC indicatesa DL CC indicated by a carrier index, by a CC index indicated in a CIF,or by a frequency index such as EARFCN. An implicit DL CC for aperiodicCSI reporting may be configured by a DL CC adjacent to the explicit DLCC. For example, if aperiodic CSI reporting is requested for specific DLCC #1, the UE may implicitly perform aperiodic CSI measurement andreporting for DL CC #2 or DL CC #0 adjacent to DL CC #1.

An adjacent DL CC index may be indexed starting from an explicitlyindicated CC in the direction of a low CC index or in the direction of ahigh CC index.

In the above-described methods, the number of implicitly indicated DLCCs for aperiodic CSI triggering is desirably one. In addition to theabove-described implicit methods, the eNB may transmit information aboutDL CCs for aperiodic CSI reporting to each UE through higher layersignaling. For example, the eNB may inform the UE of DL CCs for CSI, adirection indicating an adjacent CC index (e.g. high index order or lowindex order starting from an indicated DL CC), and the like. This isapplicable even when any one of the above-described methods (e.g. a DLCC receiving a UL grant, an SIB2 linked DL CC or DL PCC, etc.) is used.

(2) When Two or More DL CCs are Configured for Feedback

When two or more DL CCs are configured for CSI feedback, the DL CCs forCSI feedback may be selected as one of {circle around (1)} activated DLCCs, {circle around (2)} SIB2 linked DL CCs, {circle around (3)} DL CCsused for transmission of a UL grant, {circle around (4)} DL CCsindicated explicitly through higher layer (e.g. RRC layer) signaling,{circle around (5)} all DL CCs, and {circle around (6)} DL CCs allocatedimplicitly for CQI measurement.

Hereinafter, the above case {circle around (2)} will be described indetail.

A DL heavy case in which a plurality of DL CCs is allocated to one UL CChas a disadvantage of feeding back only CSI for only one DL CC, if thenumber of DL CCs having SIB2 linkage with a UL CC is one and the SIB2linked DL CCs are configured for feedback. Accordingly, it is desirablethat another DL CC be configured for feedback in addition to the SIB2linked DL CCs.

As a first example, when the eNB transmits a UL grant including a CIF tothe UE, the eNB may use the CIF to indicate a DL CC for feedback ratherthan a UL CC. Since this case corresponds to a DL heavy case, only oneUL CC is present. Accordingly, the UE may feed back CSI for an SIB2linked DL CC and DL CCs indicated by the CIF to the eNB through a PUSCH.

As a second example, when the eNB transmits a UL grant including a CIFto the UE, the eNB may use the CIF to indicate DL CCs for feedback. Thatis, the UE may sequentially report CSI for DL CCs to the eNB in a TDDform according to a specific criterion of carrier index order orfrequency order (e.g. in ascending/descending order) based on the DL CCsindicated by the CIF.

As a third example, the UE may sequentially report CSI for DL CCs to theeNB in a TDD form according to a specific criterion of carrier indexorder or frequency order (e.g. in ascending/descending order) based onDL CCs which have SIB2 linkage with a UL CC indicated by a CIF of a ULgrant.

That is, if DL CCs which have no SIB2 linked UL CC are present as in theDL heavy case, the UE transmits aperiodic CSI for SIB2 linked DL CCsfirst at a predetermined time based on the SIB2 linked DL CCs in orderto perform aperiodic CSI reporting for the corresponding DL CCs. Inaddition, the UE may sequentially transmit CSI for the DL CCs in aspecific subframe in a TDD form according to a specific criterion ofcarrier index order, frequency index order, or CIF order.

As a fourth example, the UE may use a hybrid form of the first to thirdmethods.

As a fifth example, virtual SIB2 linked DL CCs may be configured forfeedback. For example, virtual SIB2 linked UL CCs may be configured forDL CCs which have no SIB2 linkage. This virtual SIB2 linkage may beexplicitly configured by higher layer (e.g. RRC) signalling or may beimplicitly determined. When aperiodic CSI reporting is requested, the UEmay report CSI feedback for multiple SIB2 linked DL CCs or CSI feedbackfor DL CCs which have virtual SIB2 linkage with a single UL CC to theeNB.

Namely, DL CCs which have no SIB2 linkage may be configured to havevirtual SIB2 linkage. Such virtual SIB2 linkage may be indicated to theUE explicitly by higher layer signalling or implicitly. For example,virtual SIB2 linkage may be implicitly indicated in ascending ordescending order of a carrier index, cell index, CIF order, and/orfrequency index from original SIB2 linked DL CCs.

If virtual SIB2 linkage is configured and aperiodic CSI reporting istriggered, the UE may transmit CSI feedback not only for the originalSIB2 linked DL CCs but also for the virtual SIB2 linked DL CCs to theeNB. If there is a remaining code point without being used in a CIF of aUL grant (e.g. if a CIF is 3 bits, up to 8 states can be expressed and,if remaining states or bits are present after setting states for DL/ULCC indication, they may be used for code points), whether to transmitfeedback for the original SIB2 linked DL CCs or to transmit feedback forthe virtual SIB2 linked DL CCs may be indicated using the code points.If more states remain in the CIF so as to be used for code points, theeNB may inform the UE of one of the original SIB2 linked DL CCs, virtualSIB2 linked DL CCs, and all DL CCs, for which CSI feedback is to beperformed.

As described above, when a 3-bit CIF is used to indicate other DL CCsthan SIB2 linked DL CCs or UL CCs, a 1-bit CIF may remain. In this case,the eNB may inform the UE using the remaining 1-bit CIF of whether toreport CSI feedback for DL CCs indicated by the CIF, to report CSIfeedback for SIB2 linked DL CCs, or to report CSI feedback for all DLCCs.

The eNB may explicitly inform the UE of a plurality of DL CCs for whichCSI is aperiodically fed back. For example, the eNB may inform the UE ofinformation about DL CCs necessary for aperiodic CSI reporting through anew field defined in a UL grant. Alternatively, the eNB may explicitlyinform the UE of DL CCs through a CIF for the DL CCs. In this case,information about UL CCs on which a PUSCH signal is to be transmittedmay be implicitly determined by a CIF or a UL PCC. Alternatively, theeNB may indicate DL CCs for feedback using TPC of another PDCCH. The eNBmay explicitly indicate DL CCs for aperiodic CSI feedback through ULsignaling such as RRC.

A method for feeding back CSI for {circle around (6)} DL CCs allocatedimplicitly for CQI measurement will be described below.

If DL CCs which have SIB2 linkage to a UL CCs indicated by a UL grantused for an aperiodic CSI request are configured for CSI measurement andreporting, DL CCs which have SIB2 linkage with the corresponding UL CCare explicitly used for aperiodic CSI measurement and reporting.However, DL CCs which have no SIB2 linkage with the UL CC cannot performaperiodic CSI triggering. An implicit rule capable of performingaperiodic CSI triggering for such DL CCs is proposed.

For example, the UE may perform CSI measurement and reporting for a DLCC adjacent to an SIB2 linked DL CC or to a DL CC by a CIF. That is, ifaperiodic CSI for specific DL CC #1 is triggered, the eNB and UE mayconfigure a DL CC or serving cell having a carrier index or cell indexadjacent to the corresponding DL CC as a DL CC or serving cell foraperiodic CSI measurement and reporting without explicit indication.

In the embodiments of the present invention, an explicit DL CC indicatesa DL CC indicated by a carrier index, by a CC index indicated in a CIF,or by a frequency index such as EARFCN. An implicit DL CC for aperiodicCSI reporting may be configured by a DL CC adjacent to the explicit DLCC. For example, if aperiodic CSI reporting is triggered for specific DLCC #1, the UE may implicitly perform aperiodic CSI measurement andreporting for DL CC #2 or DL CC #0 adjacent to DL CC #1.

An adjacent DL CC index may be indexed starting from an explicitlyindicated CC in the direction of a low CC index or in the direction of ahigh CC index.

The number of implicitly indicated DL CCs for aperiodic CSI triggeringmay be two or more. For example, if one DL CC linked with a UL CC onwhich the UE is to transmit a PUSCH signal is an explicit DL CC for CSIreporting, the UE may perform aperiodic CSI reporting for one DL CC ormore DL CCs (e.g. two or more DL CCs) adjacent thereto.

In addition to the above-described implicit methods, the eNB maytransmit information about DL CCs for aperiodic CSI reporting to each UEthrough higher layer signaling. For example, the eNB may inform the UEof the number of DL CCs for CSI, a direction indicating adjacent CCindexes (e.g. high index order or low index order starting from anindicated DL CC), and the like. This is applicable even when any one ofthe above-described methods (e.g. DL CCs receiving a UL grant, SIB2linked DL CCs or PCCs, etc.) is used.

FIG. 11 is a diagram illustrating an aperiodic CSI reporting method in aCA environment according to an embodiment of the present invention.

In the aperiodic CSI reporting method described in FIG. 11, operationsof the eNB and UE may be changed according to a Common Search Space(CSS) or a UE-specific Search Space (USS) in which a PDCCH signal istransmitted.

The case in which the aperiodic CSI reporting method is triggered in theCSS will now be described first. In the CSS, a UL grant including anaperiodic CSI request field is set to DCI format 0. In this case, DCIformat 0 is blind-decoded by being bit-aligned with DCI format 1A.Accordingly, the size of the aperiodic CSI request field may bescheduled as one bit to prevent additional BD overhead. The followingTable 4 illustrates an exemplary aperiodic CSI request field formatwhich can be used in the embodiments of the present invention.

TABLE 4 Name Size Description Aperiodic 1 0b0: no CSI reporting isrequested CSI request bit 0b1: CSI reporting is requested. A DL CC forCSI report is configured by RRC scheduling.

In Table 4, if the CSI request field is set to ‘0’, this indicates thatno CSI reporting is requested and, if the CSI request field is set to‘1’, this indicates that CSI reporting is requested and a DL CCnecessary for CSI reporting is indicated to the UE though higher layer(e.g. RRC) signaling. In Table 4, the case in which the CSI requestfield is set to ‘1’ may indicate that aperiodic CSI reporting for all DLCCs is requested. At this time, all DL CCs may be activated DL CCs or DLCCs configured in the UE through RRC signaling.

Next, the case in which the aperiodic CSI reporting method is triggeredin the USS will be described. When the CSI reporting method is triggeredin the USS, the aperiodic CSI request field may be set to 2 bits. Thatis, one bit may be added to a DCI format used in the USS. Whileaperiodic CSI is triggered using one bit in the LTE system, it may betriggered using two bits in the LTE-A system.

This method may be applied to a PDCCH transmitted in the USS. Table 5illustrates another exemplary aperiodic CSI request field format whichcan be used in the embodiments of the present invention.

TABLE 5 Name Size Description Aperiodic 2 bits 0b00: No CSI reporting isrequested CSI request 0b01: CSI reporting for an SIB2 linked DL CC isrequested 0b10: DL CC scheduling through RRC signaling 0b11: DL CCscheduling through RRC signaling

Referring to Table 5, if the aperiodic CSI field is set to ‘00’, thisindicates that no aperiodic CSI reporting is requested. If the aperiodicCSI field is set to ‘01’, this indicates that aperiodic CSI reportingfor an SIB2 linked DL CC is requested. For example, if aperiodic CSI isset to ‘01’ in a UL grant of a PDCCH signal detected by the UE throughBD in the USS, this indicates that aperiodic CSI reporting is triggeredwith respect to a DL CC which has SIB2 linkage with a UL CC indicated bythe corresponding UL grant. In this case, the UL CC is determinedaccording to for which UL CC a PUSCH is scheduled through thecorresponding UL grant. That is, when the UE and eNB use cross-carrierscheduling, the UE may discern information about a UL CC correspondingto the UL grant received through the CIF. If cross-carrier scheduling isnot supported, a DL CC for aperiodic CSI reporting may be determined bya UL CC which has SIB2 linkage with a DL CC receiving the UL grant.

In Table 5, if the aperiodic CSI request field is set to ‘10’ or ‘11’,this indicates that aperiodic CSI reporting is triggered for CCs DL CCsallocated to the UE through higher layer (RRC) signaling.

Here, one of ‘10’ and ‘11’ of the aperiodic CSI request field mayindicate aperiodic CSI reporting for all DL CCs. That is, ‘10’ or ‘11’may indicate that aperiodic CSI reporting for all DL CCs (at this time,all DL CCs may be activated DL CCs or DL CCs configured for the UE) isrequested.

In addition, one of ‘10’ and ‘11’ of the aperiodic CSI request field inTable 5 may be configured to coincide with a combination of DL CCsconfigured through RRC signaling, indicated by ‘1’ of the aperiodic CSIrequest field of Table 4 included in the UL grant transmitted in theabove-described CSS.

Referring to FIG. 11, the eNB may transmit a UL grant including theaperiodic CSI request field described with reference to Table 4 or 5 inthe CSS or USS to the UE through a PDCCH signal (S1110).

If the aperiodic CSI request field of Table 4 is set to ‘1’ or theaperiodic CSI request field of Table 5 is set to ‘10’ or ‘11’, the eNBmay transmit higher layer signaling including information about DL CCs(or serving cells) for which aperiodic CSI reporting is to be performedto the UE (S1120).

In step S1120, information indicating DL CCs for feedback may beincluded in higher layer signaling. In the LTE-A system, a maximum of 5CCs or serving cells may configure one wideband. In this case,information about DL CCs for feedback may be included in higher layersignaling in the form of a bitmap.

For example, the information about the DL CCs for feedback may have theform of ‘10’+‘01001’. In this case, ‘10’ of a front part indicates afield value of the aperiodic CSI request field transmitted by the ULgrant of the PDCCH in step S1110 and ‘01001’ of the rear part is used toindicate DL CCs for which feedback is requested among up to 5 CCs. Eachbit of the bitmap indicates one DL CC and ‘01001’ indicates an aperiodicCSI request for the second and fifth CCs.

In 5 bits indicating DL CCs, a position of each bit may indicate each CCaccording to a CC index, a frequency index, or a CIF value of CCsconfigured by the UE. For example, when 5 CCs configured by the UE aref1, f2, f3, f4, and f5 (where (f1<f2<f3<f4<f5), each bit of ‘01001’indicates f1, f2, f3, f4, and f5 starting from the beginning.

The bitmap information may be configured for DL CCs configured by the UEor activated DL CCs. When the eNB configures the bitmap information, itis possible to indicate effective information starting from the locationof an MSB of a bitmap. If only 3 activated or configured DL CCs of acertain UE are present, all of the 5 bits need not be used. Accordingly,it is desirable to configure bitmap information such that effectiveinformation may be transmitted from the location of an MSB of a bitmapsuch as ‘101xx’ among 5 bits of ‘xxxxx’.

If there are remaining or unused bits caused by DL CCs which are notconfigured or activated among 5 bits used to indicate DL CCs for anaperiodic CSI report request, the corresponding bits are always set to‘0’, thereby eliminating an error or ambiguity of the UE. Therefore, theabove ‘101xx’ may be desirably set to ‘10100’.

Referring back to FIG. 11, the UE may confirm which DL CCs (servingcells) are used for aperiodic CSI measurement and reporting throughhigher layer signaling in step S1120 (S1130).

If the first and third DL CCs are used for aperiodic CSI feedback as inthe above example, the UE may measure channel quality for the first andthird DL CCs and generate associated CSI (S1140).

The UE may feed back the generated aperiodic CSI report to the eNBthrough a PUSCH region (S1150).

In step S1110, if the aperiodic CSI request field of Table 4 is set to‘0’ or the aperiodic CSI request field of Table 5 is set to ‘00’, the UEperforms only a periodic CSI report operation without performing anaperiodic CSI report operation. In this case, the UE may report CSI tothe eNB not through the PUSCH region but through a PUCCH region.

In step S1110, if the aperiodic CSI request field of Table 5 is set to‘01’, CSI may be measured with respect to an SIB2 linked DL CCirrespective of higher layer signaling of step S1120 and the aperiodicCSI report operation may be performed.

FIG. 12 is a diagram illustrating a UE and an eNB in which theembodiments of the present invention described with reference to FIG. 1to FIG. 11 can be performed, according to another embodiment of thepresent invention.

The UE may operate as a transmitter in UL and as a receiver in DL. TheeNB may operate as a receiver in UL and as a transmitter in DL.

The UE and eNB may include Transmit (Tx) modules 1240 and 1250 andReceive (Rx) modules 1250 and 1270, respectively, for controllingtransmission and reception of information, data, and/or messages, andmay include antennas 1200 and 1210, respectively, for transmitting andreceiving the information, data, and/or messages.

The UE and eNB may include processors 1220 and 1230 for performing theabove-described embodiments of the present invention and memories 1280and 1290 for temporarily or permanently storing a processing procedureperformed by the processors, respectively. The UE and eNB of FIG. 12 mayfurther include one or more of an LTE module for supporting the LTEsystem and the LTE-A system and a low-power Radio Frequency(RF)/Intermediate Frequency (IF) module.

The Tx modules and Rx modules included in the UE and the eNB may performa packet modulation/demodulation function for data transmission, a quickpacket channel coding function, Orthogonal Frequency Division MultipleAccess (OFDMA) packet scheduling, Time Division Duplex (TDD) packetscheduling, and/or a channel multiplexing function.

The apparatus described in FIG. 12 is a means for implementing themethods described with reference to FIG. 1 to FIG. 11. The embodimentsof the present invention may be performed using constituent elements andfunctions of the aforementioned UE and eNB.

For example, the processor of the UE may receive a PDCCH signalincluding a UL grant and/or a CIF by monitoring a USS or CSS.Especially, an LTE-A UE may receive the PDCCH signal without blockingthe PDCCH signal with another LTE UE by performing BD for an extendedCSS. The processor of the UE may confirm DL CCs or serving cell for CSImeasurement and control CSI measurement and aperiodic CSI reporting forcorresponding DL CCs, by confirming an aperiodic CSI report requestfield received from the eNB.

Meanwhile, the UE in the present invention may be any of a PersonalDigital Assistant (PDA), a cellular phone, a Personal CommunicationService (PCS) phone, a Global system for Mobile (GSM) phone, a WidebandCDMA (WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-heldPC, a notebook PC, a smartphone, a Multi Mode-Multi Band (MM-MB)terminal, etc.

The smartphone is a terminal mixing the advantages of both a mobilecommunication terminal and a PDA and may refer to a terminal in whichdata communication functions such as scheduling management, faxtransmission and reception, and Internet access, which are functions ofthe PDA, are incorporated into the mobile communication terminal. TheMM-MB terminal refers to a terminal which has a multi-modem chip thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g., a CDMA 2000 system, a WCDMA, etc.).

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof.

In a hardware configuration, the embodiments of the present inventionmay be achieved by one or more Application Specific Integrated Circuits(ASICs), Digital Signal Processors (DSPs), Digital Signal ProcessingDevices (DSPDs), Programmable Logic Devices (PLDs), Field ProgrammableGate Arrays (FPGAs), processors, controllers, microcontrollers,microprocessors, etc.

In a firmware or software configuration, the embodiments of the presentinvention may be achieved by a module, a procedure, a function, etc.performing the above-described functions or operations. For example,software code may be stored in the memory units 1280 and 1290 andexecuted by the processors 1220 and 1230. The memory units are locatedat the interior or exterior of the processor and may transmit data toand receive data from the processor via various known means.

The embodiments of the present invention may be carried out in otherspecific ways without departing from the spirit and essentialcharacteristics of the present invention. Accordingly, the abovedetailed description is therefore to be construed in all aspects asillustrative and not restrictive. The scope of the invention should bedetermined by the appended claims and their legal equivalents, not bythe above description, and all changes coming within the meaning andequivalency range of the appended claims are intended to be embracedtherein. Also, claims that are not explicitly cited in the appendedclaims may be presented in combination as an exemplary embodiment of thepresent invention or included as a new claim by subsequent amendmentafter the application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention may be applied to variouswireless access systems, for example, a 3GPP LTE system, a 3GPP LTE-Asystem, a 3GPP2 system, and/or an IEEE 802.xx system. The embodiments ofthe present invention may be applied not only to the above variouswireless access systems but also to all technical fields applying thevarious wireless access systems.

The invention claimed is:
 1. A method for aperiodically feedback channelstate information (CSI) in a wireless access system supportingmulticarrier aggregation, the method comprising: receiving, by a userequipment (UE) from a base station (BS), a radio resource control (RRC)signal indicating two or more cells which an aperiodic CSI feedback isto be triggered; receiving, by the UE from the BS, an uplink grantincluding a CSI request field, the CSI request field indicating that thetwo or more cells are triggered for the aperiodic CSI feedback; andtransmitting, by the UE to the BS, a physical uplink shared channel(PUSCH) including the aperiodic CSI feedback for the two or more cellsindicated by the RRC signal.
 2. The method according to claim 1, furthercomprising: measuring the CSI of the two or more cells indicated by theRRC signal.
 3. The method according to claim 1, wherein the CSI requestfield is included in a downlink control information (DCI) format
 0. 4.The method according to claim 1, wherein the PUSCH is transmitted foursubframes after receiving the uplink grant.
 5. The method according toclaim 1, wherein a size of the CSI request field is set to 2 bits forindicating that the two or more cells are triggered for the aperiodicCSI feedback.
 6. A method for receiving aperiodically feedback channelstate information (CSI) in a wireless access system supportingmulticarrier aggregation, the method comprising: transmitting, by a basestation (BS) to a user equipment (UE), a radio resource control (RRC)signal indicating two or more cells which an aperiodic CSI feedback isto be triggered; transmitting, by the BS to the UE, an uplink grantincluding a CSI request field, the CSI request field indicating that thetwo or more cells are triggered for an aperiodic CSI feedback; andreceiving, by the BS from the UE, a physical uplink shared channel(PUSCH) including the aperiodic CSI feedback for the two or more cellsindicated by the RRC signal.
 7. The method according to claim 6, whereinthe CSI request field is included in a downlink control information(DCI) format
 0. 8. The method according to claim 6, wherein the PUSCH isreceived four subframes after receiving the PDCCH signal.
 9. The methodaccording to claim 6, wherein a size of the CSI request field is set to2 bits for indicating that the two or more cells are triggered for theaperiodic CSI feedback.
 10. A user equipment (UE) for aperiodicallyfeedback channel state information (CSI) in a wireless access systemsupporting multicarrier aggregation, the UE comprising: a transmitter; areceiver; and a processor for supporting an aperiodically feedback theCSI, wherein processor controls the receiver to receive, from a basestation (BS), a radio resource control (RRC) signal indicating two ormore cells which the aperiodic CSI feedback is to be triggered; receive,from the BS, an uplink grant including a CSI request field indicatingthat two or more cells are triggered for the aperiodic CSI feedback; andwherein the processor controls the transmitter to transmit, to the BS, aphysical uplink shared channel (PUSCH) including the aperiodic CSIfeedback for the two or more cells indicated by the RRC signal.
 11. Theuser equipment according to claim 10, wherein the processor furthermeasures the CSI of the two or more cells indicated by the RRC signal.12. The user equipment according to claim 10, wherein the CSI requestfield is included in a downlink control information (DCI) format
 0. 13.The user equipment according to claim 10, wherein the PUSCH istransmitted four subframes after receiving the PDCCH signal.
 14. Theuser equipment according to claim 10, wherein a size of the CSI requestfield is set to 2 bits for indicating that the two or more cells aretriggered for the aperiodic CSI feedback.
 15. A base station (BS) forreceiving aperiodically feedback channel state information (CSI) in awireless access system supporting multicarrier aggregation, the BScomprising: a transmitter; a receiver; and a processor for supporting toreceive an aperiodically feedback the CSI, wherein the processorcontrols the transmitter to transmit, to a user equipment (UE), a radioresource control (RRC) signal indicating two or more cells which theaperiodic CSI feedback to be triggered; and transmit, to the UE, anuplink grant including a CSI request field indicating that the two ormore cells are triggered for the aperiodic CSI feedback, and wherein theprocessor further controls the receiver to receive, from the UE, aphysical uplink shared channel (PUSCH) including the aperiodic CSIfeedback for the two or more cells indicated by the RRC signal.
 16. Thebase station according to claim 15, wherein the CSI request field isincluded in a downlink control information (DCI) format
 0. 17. The basestation according to claim 15, wherein the PUSCH is received foursubframes after receiving the PDCCH signal.
 18. The base stationaccording to claim 15, wherein a size of the CSI request field is set to2 bits for indicating that the two or more cells are triggered for theaperiodic CSI feedback.